Property tax starts with your assessor's estimate of what your home is worth, then multiplies that value by your local tax rate

Property tax is not based on what you paid for your house or what you could sell it for today. It is based on an assessed value — a number your county or municipal assessor decides — multiplied by a tax rate set by your local government. The assessed value is usually lower than market value. The tax rate varies by location and can change year to year. Your bill arrives once a year (or twice, depending on where you live), and the math behind it follows the same basic steps everywhere, though the names and timing differ by state.

Understanding how this calculation works helps you read your bill, know when to challenge it, and plan for the cost. The process has three moving parts: the assessed value, the tax rate, and the timing of payment. Each one can change, and each one affects what you owe.

Key Takeaways

  • Your assessor estimates your home's value by comparing it to similar homes that sold recently, looking at the condition and size of your property, or using a formula based on income if it is a rental.
  • The assessed value is multiplied by a tax rate (called a millage rate or tax rate) set by your city, county, or school district to produce your tax bill.
  • You can challenge your assessment if you believe the value is wrong, usually by filing a formal objection with your assessor's office within a set window each year.
  • Property tax bills are due on dates set by your local government, and paying late triggers penalties and interest that compound monthly.
  • Your assessed value can change every year or every few years depending on your state's reassessment schedule.

How assessors determine your home's assessed value

Your assessor uses one of three main methods to arrive at a number. The most common is the sales comparison approach: the assessor looks at homes similar to yours that sold in your area within the past year or two, adjusts for differences (your house has a garage, that one does not), and estimates what yours would sell for. This number is then adjusted downward to create the assessed value, which is typically 80 to 90 percent of estimated market value, though this percentage varies by state.

The second method is the cost approach, used when few comparable sales exist. The assessor estimates what it would cost to rebuild your house from scratch, subtracts depreciation based on age and condition, and adds the land value. This method is common in rural areas or for unusual properties.

The third method is the income approach, used almost always for rental properties and commercial buildings. The assessor estimates how much rent the property could generate per year, then divides by a standard capitalization rate to arrive at a value. A house that rents for $1,500 a month might be valued at $300,000 using this method, depending on local rates.

Most assessors use a mix of these methods. Your assessor's office should have a public record of how they valued your property — you can request this document, often called a property record card or assessment worksheet. This record shows which method was used and what comparable sales or cost data supported the final number.

The tax rate and how it produces your bill

Once your assessed value is set, your local government applies a tax rate to it. This rate is expressed as a dollar amount per $1,000 of assessed value (or sometimes per $100). If your home is assessed at $300,000 and your tax rate is $12 per $1,000 of value, your calculation is: ($300,000 ÷ $1,000) × $12 = $3,600 per year.

Tax rates are set by your city council, county commission, or school board — or a combination of all three. Your property tax bill often funds multiple entities: your county, your city or township, your school district, and sometimes a fire district or library district. Each entity sets its own rate, and they are added together. A single property tax bill might show five or six line items, each representing a different taxing body.

Tax rates change year to year based on how much money each entity needs to spend and how much total assessed value exists in the district. If your school district needs $50 million and the total assessed value of all homes in the district is $5 billion, the rate is $10 per $1,000. If assessed values rise the next year to $5.2 billion and the district still needs $50 million, the rate falls to $9.62 per $1,000. This means your bill can drop even if your own assessed value stays the same.

When your assessed value changes

Your assessed value does not stay the same forever. Most states reassess all properties every year, though a few reassess every two, three, or four years. Some states allow assessments to rise only by a set percentage each year (called a cap or homestead exemption limit), even if the market value has risen more.

You will receive a notice when your assessment changes — the timing and format vary by state. Some states send the notice in spring, others in fall. Read it carefully: it will show your previous assessed value, your new assessed value, and the reason for the change (market adjustment, physical change to the property, or reassessment cycle). If you disagree with the new value, you have a limited window to file an objection, usually 30 to 60 days from the notice date.

If you made improvements to your home — added a deck, finished a basement, replaced the roof — your assessor may increase your assessed value to reflect the improvement. You can request a reassessment if you made repairs that restored the home to its previous condition rather than improving it, though the burden is on you to prove the distinction.

How to challenge your assessment

If you believe your assessed value is too high, you can file a formal objection. The process and important date vary by state, but the general steps are the same. First, gather evidence: recent sales of comparable homes in your area, a professional appraisal if you have one, photos of any damage or deferred maintenance, or documentation of recent repairs. Your county assessor's office can tell you what evidence they accept.

Next, file your objection by the important date. Most states require a written form, available from your assessor's office or online. Some states allow you to file online; others require a paper form mailed or delivered in person. The important date is usually 30 to 60 days after you receive your assessment notice, though a few states allow objections year-round.

After you file, your assessor may schedule a meeting with you to discuss your objection. Bring your evidence. If you and the assessor cannot agree, most states allow you to appeal to a county board of review or assessment appeals board. This board is separate from the assessor's office and hears objections from property owners. If you still disagree after the board's decision, you can appeal to court, though this is expensive and most people do not pursue it.

When your property tax bill is due and what happens if you pay late

Property tax bills are due on dates set by your local government, usually once or twice per year. Some states bill in spring and fall; others bill once in winter. Your bill will show the due date clearly. If you own your home outright, you pay the assessor's office or tax collector directly. If you have a mortgage, your lender may collect property tax as part of your monthly payment and pay it from an escrow account.

If you pay late, penalties and interest begin to accrue when ready. Penalties are typically 5 to 10 percent of the unpaid amount, and interest compounds monthly at a rate set by state law (usually 6 to 12 percent per year). A $3,600 bill paid 60 days late might cost you an extra $150 to $200 in penalties and interest. If you do not pay for several years, your county can place a lien on your property or, in some cases, foreclose and sell it to recover the unpaid taxes.

If you cannot pay by the due date, contact your tax collector's office when ready. Many jurisdictions offer payment plans, deferral programs for seniors or disabled homeowners, or temporary relief during hardship. The sooner you reach out, the more options you may have.

Exemptions and reductions that lower your bill

Many states and localities offer exemptions that reduce your assessed value or your tax bill. The most common are homestead exemptions, which reduce the assessed value of your primary residence by a set amount (often $25,000 to $50,000, though this varies widely). To claim a homestead exemption, you typically file a form with your assessor's office, usually once, though some states require annual renewal.

Other exemptions exist for seniors, disabled homeowners, veterans, and agricultural land. may be able to access and the amount of the reduction vary by state and county. Your assessor's office maintains a list of available exemptions and the forms needed to claim them. If you think you may may have access to, ask your assessor directly — they can tell you whether you are may be able to access and what documents to submit.

Some states also offer tax credits or rebates separate from exemptions. These are usually claimed on your state income tax return rather than through your assessor's office. Check your state's revenue or taxation website to see what programs exist in your state.

Frequently Asked Questions

Why is my assessed value so different from what I paid for my house?

Assessed value and purchase price are calculated differently. Your purchase price reflects what you and the seller agreed on at that moment; assessed value reflects what the assessor estimates the home is worth for tax purposes, using recent sales of similar homes. If you bought your house years ago, market values may have risen or fallen significantly. If you bought it recently, the assessed value may lag behind your purchase price by a year or more, since assessments are based on past sales data.

Can my property tax bill change if I do not make any changes to my house?

Yes. Your assessed value can change because of market conditions — if homes in your area are selling for more, your assessment may rise. Your tax rate can also change year to year based on how much money your city, county, or school district needs to spend. Both changes result in a higher or lower bill even if your house itself has not changed.

What happens if I disagree with my assessment and file an objection?

Your assessor will review your objection and the evidence you submit. If they agree the value is wrong, they will lower your assessment. If they disagree, you can appeal to your county's board of review or assessment appeals board, which will hold a hearing and make a final decision. You can then appeal to court if you wish, though this is costly and rarely pursued.

Do I have to pay property tax if I own my home outright?

Yes. Property tax is owed by anyone who owns real estate, whether the property is paid off or financed. If you have a mortgage, your lender collects the tax from your monthly payment and pays it on your behalf. If you own the home outright, you pay the tax collector directly.

What is the difference between assessed value and market value?

Market value is what your home would sell for on the open market today. Assessed value is what your assessor estimates for tax purposes, usually lower than market value. The assessor uses recent sales of comparable homes to estimate market value, then applies a standard percentage (often 80 to 90 percent) to arrive at assessed value. This keeps tax bills lower than they would be if based on full market value.